1. Field of Application
The present invention relates to a brush support jig which is used when mounting the brush assembly of a rotary electric machine, and to a method of mounting a brush assembly by using such a brush support jig.
2. Related Prior Art
In a rotary electric machine having slip rings and brushes which respectively contact the slip rings, such as an AC generator of a motor vehicle, a brush assembly is mounted on the machine, which includes a brush holder for supporting the brushes and also includes a slip ring cover which is of box configuration and which, together with the brush holder, surrounds the peripheries of the slip rings. If there is a defect such as a surface scratch in the slip rings, then this can cause abnormal noise to be generated and can result in shortening of the operating life of the brushes. For that reason, it is important to ensure that no damage occurs to the slip rings when the brush assembly is being mounted.
Various types of brush support jig have been used in the prior art, with the objective of retaining the brushes in such a manner as to prevent damage to the slip rings when the brush assembly is being mounted, i.e., to restrain the brushes against motion towards the slip rings during the mounting operation. An example of this is shown in FIG. 6, in which before the brushes are mounted at the peripheries of the slip rings 134, 135, a brush support jig 151 which is of pin configuration is inserted into the brush holder 127, to prevent the brushes 128, 129 (which are being pushed towards the slip rings by the springs 144, 145 respectively) from flying out. In the following, it should be understood that the term “pin configuration” or “pin-shaped” as applied to a brush support jig is used to signify that the jig is basically of narrow elongated form, having width and depth dimensions which are each substantially smaller than the circumference of the slip rings. With this prior art example, the brush support jig 151 is formed of a wire which is made of a hard material such as steel, with a diameter of approximately 2 mm. A sufficiently large spacing (e.g., approximately 3 mm) is formed between the brush support jig 151 and the slip rings 134, 135 to ensure that the brush support jig 151 will not contact and thereby damage the slip rings during the mounting operation. The brush support jig 151 is supported at support regions that are respectively constituted by a metal member 127a which is mounted centrally in the brush holder 127 and by a hole 102a which is formed in the rear-side frame 102.
In the case of Japanese Patent 63-310349 (1998), an arrangement for preventing the brushes of a rotary electric machine from flying out, when the brush assembly is being mounted on the machine, is implemented by a pin-configuration brush support jig which is inserted into holes respectively formed in the brushes, with the brush support jig being supported at support regions constituted by these holes in the brushes and by a hole which is formed in a rear-side frame of the rotary electric machine. With that prior art example, even if the brush support jig should become tilted, the brushes are effectively prevented from contacting the slip rings.
Furthermore in Japanese Patent 9-117110 (1997), it is proposed to fit a brush support jig which is of tubular configuration (having an inner diameter which is greater than the outer diameter of the slip rings) into the inner periphery of a cylindrical aperture which is formed in the brush holder and in the slip ring cover, so that the brush support jig surrounds the peripheries of the slip rings and thereby restrains the brushes from contacting the slip rings, when the brush assembly is being mounted.
However in the case of the prior art configuration shown in FIG. 6, due to the manner in which the brush support jig is supported, it is necessary for the brush support jig to be of substantially large diameter, in order to have sufficient rigidity to withstand the force exerted by the springs against the brushes (in particular, the spring 144, acting on the brush 128, as can readily be understood from FIG. 6). Thus, the spacing between the slip rings and brush support jig must be relatively large, and hence the overall size of the brush assembly becomes large. For that reason, such a configuration is not suited to the present-day requirements for greater compactness.
In the case of the configuration disclosed in Japanese Patent 63-310349 (1998), in order to prevent the operating life of the brushes from being shortened as a result of the fact that holes must be formed in the brushes, it is necessary to increase the length of the brushes accordingly. For that reason, the brush assembly becomes large in size, so that the present-day requirements for greater compactness cannot be satisfied by such an arrangement.
In the case of the configuration disclosed in Japanese Patent 9-117110 (1997), it is necessary to form a large opening in the brush assembly, adjacent to the outer end of the slip rings, and this opening must be covered by a seal, such as a rubber seal, after the brush assembly has been mounted and the brush support jig has been removed. However due to manufacturing deviations in the shapes of components such as the slip ring cover, the rubber seal may not be pressed evenly around the rim of the slip ring cover, so that an effective seal cannot be ensured. Moreover, due to changes in elasticity which will occur in the rubber seal, the cross-sectional area of a ventilation path which includes the rubber seal may be reduced, so that cooling ventilation of the areas of sliding contact between the slip rings and brushes may become insufficient.